Patent application title: DISPLAY AND ELECTRONIC APPARATUS EQUIPPED WITH SAME

Abstract:

An active matrix display capable of compensating leaking current while
maintaining the aperture rate is provided. The active matrix display
device has a plurality of pixels arranged as a matrix, and each of the
pixels includes a liquid crystal display element; a driving control
switch for controlling the driving of the liquid crystal display element;
and a storage capacitor for storing image data provided to the liquid
crystal display element via the driving control switch. The display
device is an active matrix display device comprising voltage-compensating
means for applying a specified voltage to one end of the storage
capacitor opposite to another end coupled to the liquid crystal display
element in a maintaining period.

Claims:

1. An active matrix display device having a plurality of pixels arranged
as a matrix, each of the pixels comprising:a liquid crystal display
element;a driving control switch for controlling the driving of the
liquid crystal display element; anda storage capacitor for storing image
data provided to the liquid crystal display element via the driving
control switch;wherein the display device is an active matrix display
device comprising voltage-compensating means for applying a specified
voltage to one end of the storage capacitor opposite to another end
coupled to the liquid crystal display element in a maintaining period.

2. The active matrix display device according to claim 1 wherein the
voltage-compensating means has the specified voltage change at multiple
levels in the maintaining period according to previously programmed
voltage steps.

3. The active matrix display device according to claim 2 wherein the
voltage-compensating means has the specified voltage linearly change in
the maintaining period.

4. The active matrix display device according to claim 1 wherein the
voltage-compensating means applies the specified voltage to the storage
capacitor via the CS lines.

5. The active matrix display device according to claim 1 wherein the
voltage-compensating means includes:a voltage source for providing the
specified voltage;a voltage-step storing member for storing previously
programmed voltage steps; anda power control member for controlling the
voltage source in order to having the specified voltage change at
multiple levels in the maintaining period according to previously
programmed voltage steps.

Description:

[0001]The present invention relates to an active matrix display including
a plurality of pixels arranged as a matrix, and an electronic apparatus
equipped with such a display.

BACKGROUND OF THE INVENTION

[0002]In general, in an active matrix display utilizing liquid crystal
display elements, each pixel is disposed with a switch for controlling
the writing of image data into the liquid crystal display elements and a
storage capacitor for storing data within a writing and switching period
of the image data. However, the image data held as charges in the
capacitor is subject to loss with time due to leaking current. The
leaking current causes reduction in a pixel voltage and renders flicker.

[0003]For example, the PCT Japanese Patent Publication No. 2004-518993
discloses a technique for reducing leaking current from a storage
capacitor.

[0004]In the prior art, the effect of leaking current is compensated by
enlarging the capacity of the storage capacitor or inserting an
amplifying circuit between the storage capacitor and the liquid crystal
display element. Then a problem of reduced pixel aperture rate may be
encountered. Take a transmissive LCD with a backlight source for
illumination from the back side as an example. Once the pixel aperture
rate is reduced, the illuminance of the backlight source needs to be
higher, and thus power consumption is increased.

[0005]In view of the problem encounter in the prior art, an object of the
present invention is to provide an active matrix display capable of
compensating leaking current while maintaining the aperture rate and an
electronic apparatus equipped with such a display.

SUMMARY OF THE INVENTION

[0006]In order to achieve the object mentioned above, there is provided an
active matrix display device having a plurality of pixels arranged as a
matrix, each of the pixels comprising: a liquid crystal display element;
a driving control switch for controlling the driving of the liquid
crystal display element; and a storage capacitor for storing image data
provided to the liquid crystal display element via the driving control
switch. The display device is an active matrix display device comprising
voltage-compensating means for applying a specified voltage to one end of
the storage capacitor opposite to another end coupled to the liquid
crystal display element in a maintaining period.

[0007]In this way, the leaking current problem occurring in the
maintaining period can be remedied, and the flicker problem can be
ameliorated. Furthermore, according to this example, since there is no
modification in the pixel structure, a pixel aperture rate comparable to
prior art can be kept.

[0008]In an embodiment of the invention, the voltage-compensating means
has the specified voltage change at multiple levels in the maintaining
period according to previously programmed voltage steps. Preferably, the
voltage-compensating means has the specified voltage linearly change in
the maintaining period.

[0009]In this way, optimal compensating operations for leaking current can
be determined depending on uses and ambient conditions of the display
device, implementation of the switch element as the driving control
switch, and the function of the controller.

[0010]In an embodiment of the invention, the voltage-compensating means
applies the specified voltage to the storage capacitor via the CS lines.

[0011]In this way, the structure is simplified as existent CS lines are
used. Nevertheless, it is required in this embodiment that the CS lines
are independent for different rows.

[0012]In an embodiment of the invention, the voltage-compensating means
includes: a voltage source for providing the specified voltage; a
voltage-step storing member for storing previously programmed voltage
steps; and a power control member for controlling the voltage source in
order to having the specified voltage change at multiple levels in the
maintaining period according to previously programmed voltage steps.

[0013]According to an embodiment of the present invention, the active
matrix display device can be used in an electronic apparatus equipped
with a display device for prompting users. Examples include a laptop PC,
mobile phone, portable personal digital assistant (PDA), car navigation
device or portable game set.

[0014]According to the present invention, it is able to provide an active
matrix display capable of compensating leaking current while maintaining
the aperture rate and an electronic apparatus equipped with such a
display.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 illustrates an example of an electronic apparatus equipped
with a display device according to an embodiment of the present
invention.

[0016]FIG. 2 illustrates construction of a display device according to an
embodiment of the present invention.

[0017]FIG. 3 illustrates construction of a pixel according to an
embodiment of the present invention.

[0018]FIG. 4 illustrates construction of a voltage-compensating member
according to an embodiment of the present invention.

[0019]FIG. 5A is a timing chart illustrating a first example of
compensating operation for leaking current by a voltage-compensating
member according to an embodiment of the present invention.

[0020]FIG. 5B is a timing chart illustrating a second example of
compensating operation for leaking current by a voltage-compensating
member according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021]Hereinafter, embodiments according to the present invention are
described with reference to the accompanying drawings.

[0022]FIG. 1 illustrates an example of an electronic apparatus equipped
with a display device according to an embodiment of the present
invention. The electronic apparatus 100 as shown in FIG. 1 is a laptop
PC. Alternatively, it can also be another electronic apparatus, e.g. a
mobile phone, portable personal digital assistant (PDA), car navigation
device or portable game set. The electronic apparatus 100 has a display
device 10 which includes a display module for displaying images, etc.

[0023]FIG. 2 illustrates construction of a display device according to an
embodiment of the present invention. The display device 10 as shown in
FIG. 2 includes a display module 20, a source drive 22, a gate driver 24,
a voltage-compensating member 26 and a controller 28.

[0024]In the display module 20, at least one liquid crystal display
element is disposed at an intersect of a source line 12 and a gate line
14. The source driver 22 is connected to each of the pixels though the
source line 12 for providing image data to the pixels. The gate driver 24
controls ON/OFF of each pixel via the gate line 14. The
voltage-compensating member 26 is connected to each of the pixels through
a voltage-compensating line 16 for providing an offset voltage for each
pixel for leaking current compensation. The controller 28 synchronizes
the source driver 22, gate deriver 24 and voltage-compensating member 26,
and controls their operations.

[0025]FIG. 3 illustrates construction of a pixel according to an
embodiment of the present invention. The pixel 30 as shown in FIG. 3 is
disposed with a liquid crystal display element 32, a driving control
switch 34 for controlling the driving of the liquid crystal display
element 32, and a storage capacitor 36 for storing image data provided to
the liquid crystal display element 32 via the driving control switch 34.

[0026]The liquid crystal display element 32 has one end coupled to a
common electrode CE, and another end coupled to the source line 12 via
the driving control switch 34. The driving control switch 34, e.g. a thin
film transistor (TFT), connects the control terminal to the gate line 14.
When the gate line 14 is at a high level, the driving control switch 34
is switched on so as to apply a voltage of the source line 12 to the
liquid crystal display element 32.

[0027]The storage capacitor 36 has one end coupled to the connection of
the liquid crystal display element 32 and the driving control switch 34,
and another end coupled to the voltage-compensating line 16. In this
embodiment, a CS line coupled to the storage capacitor 36 in a general
pixel structure may be used as the voltage-compensating line 16. However,
in this embodiment, CS lines in different rows should be independent.
When the gate line 14 is at a low level and during the driving control
switch is switched off, the storage capacitor 36 maintains the voltage
applied to the liquid crystal display element 32 via the driving control
switch 34 in the form of charges. Actually, charges stored in the storage
capacitor 36 would be subject to loss with time as leaking current
flowing to the source line 12 via the driving control switch 34. In order
to compensate the leaking current, a specified voltage is applied to the
storage capacitor 36 via the voltage-compensating line 16 by the
voltage-compensating member 26 in the voltage-maintaining period.
Concretely, by way of capacity coupling to the storage capacitor 36, the
potential level at the connection of the liquid crystal display element
32 and the driving control switch 34, accurately at the end of the liquid
crystal display element 32 opposite to the end coupled to the common
electrode, is shifted so as to compensate the leaking current.

[0028]FIG. 4 illustrates construction of a voltage-compensating member
according to an embodiment of the present invention. The
voltage-compensating member 26 shown in FIG. 4 includes a voltage source
40 for providing a specified voltage to each of the pixels via the
voltage-compensating line 16, a power control member 42 for controlling
the voltage source 40 according to a control signal from the controller
28, and a voltage-step storing member 44 for storing previously
programmed voltage steps.

[0029]The voltage source 40 is a variable voltage source capable of
changing voltages with multi-levels or linearly. The power control member
42 receives from the controller 28 a control signal that indicates that
an offset voltage is to be provided for pixels in the voltage-maintaining
period, and has the voltage supplied from the voltage source 40 changed
according to a previously programmed voltage step stored in the
voltage-step storing member 44.

[0030]The voltage steps are set when the display device 10 is made
according to uses and ambient conditions of the display device 10,
implementation of the switch element as the driving control switch 34,
and the function of the power control member 42. Hereinafter, the
compensating operations for leaking current by the voltage-compensating
member 26 will be described according to a variety of voltage steps.

[0031]FIG. 5A is a timing chart illustrating a first example of
compensating operation for leaking current by a voltage-compensating
member according to an embodiment of the present invention. In FIG. 5A,
changes of a gate signal (a), a CS voltage (b) and a pixel voltage (c)
with time are shown sequentially.

[0032]The gate signal is a signal provided from the gate driver 24 to the
control terminal of the driving control switch 34 of the pixel 30 via the
gate line 14. In this embodiment, the high level of the gate signal
renders the ON state of the driving control switch 34. Once the driving
control switch 34 is switched on, a voltage indicative of image data
provided from the source driver 22 via the source line 12 is applied to
the liquid crystal display element 32.

[0033]The CS voltage is a voltage provided from the voltage-compensating
member 26 to the storage capacitor of the pixel 30 via the
voltage-compensating line 16 (i.e. the CS line in this embodiment).
According to prior art, when the gate signal is at a low level and during
the off period of the driving control switch 34 (i.e. the
voltage-maintaining period), the CS voltage is constant as indicated by
the dashed line in the drawing. In contrast, according to this
embodiment, the CS voltage in the voltage-maintaining period, as
indicated by the solid line in the drawing, linearly increases or
decreases with a specified slope.

[0034]The pixel voltage is a voltage at the connection of the liquid
crystal display element 32 and the driving control switch 34, accurately
at the end of the liquid crystal display element 32 opposite to the end
coupled to the common electrode. The voltage is stored in the storage
capacitor 36 in the form of charges in the voltage-maintaining period.
According to prior art, charges stored in the storage capacitor 36 would
be subject to loss with time as leaking current flowing to the source
line 12 via the driving control switch 34. Therefore, the pixel voltage
would decay as indicated by the dash lines in the drawing. In contrast,
according to this embodiment, the pixel voltage will not decay, and
instead, is kept constant, as indicated by the solid lines in the
drawing. It results from a specified voltage ΔVcom, linearly
increasing or decreasing with a specified slope, which is applied to one
end of the storage capacitor 36 opposite to the end coupled to the liquid
crystal display element 32.

[0035]FIG. 5B is a timing chart illustrating a second example of
compensating operation for leaking current by a voltage-compensating
member according to an embodiment of the present invention. In FIG. 5B,
changes of a gate signal (a), a CS voltage (b) and a pixel voltage (c)
with time are shown sequentially.

[0036]In this example, the CS voltage, as indicated by the solid line in
the drawing, changes to another constant value at specified time points
(T1 and T2) in the voltage-maintaining period. Accordingly, the pixel
voltage, as indicated by the solid line in the drawing, will decay with
leaking current prior to the specified time points (T1 and T2) in the
voltage-maintaining period, just like the prior art. However, once the
specified time points are reached, only increase or decrease amount
equivalent to the variation amount ΔVcom, of the CS voltage
for compensating the decay is involved.

[0037]In this way, the voltage-compensating member 26 according to an
embodiment of the present invention applies a constant voltage to the end
of the storage capacitor 36 opposite to the end coupled to the liquid
crystal display element 32, thereby compensating the pixel voltage drop
rendered by leaking current. As a result, the flicker problem caused by
pixel voltage drop can be avoided. Furthermore, according to this
example, there is no modification in the pixel structure so as to
maintain the pixel aperture rate.

[0038]The invention is described as above based on preferred embodiments,
but is not limited to the embodiments as described. Instead, modification
or change may be made within the scope of the invention.

[0039]For example, the voltage-compensating member 26 in the above
embodiments receives a control signal from the controller 28 and feeds an
offset voltage to each pixel according to previously programmed voltage
steps. Alternatively, the voltage-compensating member 26 may be
configured to be able to directly receive a signal indicating a high/low
state of the gate signal from the gate driver 24.

[0040]Furthermore, although the voltage-compensating lines 16 in the above
embodiments are disposed in each row of the pixel matrix, the
voltage-compensating lines 16 can also be disposed in each column or each
pixel instead of in each row, depending on the driving mode of the
display device, e.g. dot inversion driving, horizontal or vertical
inversion driving or frame inversion driving.